Best explanation of what chromatography is. IMHO.

When I have to explain how chromatography works to someone, I use a “Theoretical Model” I stole copied from Ralph Calvert of http://www.itsjustabox.com/

The theory (which I modified) starts with:

Retention

Basically, imagine a corridor in a shopping mall with many shops, full of people, and all of them are going to the restaurant in the back. Then a large group of friends enter, and agree to meet at the same restaurant for lunch.

Now consider this:

-When they enter the corridor, this is the injection.

-The corridor is the chromatographic column.

-In this model, the group of friends are the analytes, the compounds that need to be separated. Each friend has different caracteristics, different tastes for window shopping.

-These shops are the active sites where the retention effects (interactions) take place.

-The people that do not belong to the group of friends or family acts like mobile-phase. They not only carry (push) the friends group forward but also interact with shops displacing whoever is looking at the shop window.

-The restaurant is the detector.

With this in mind. imagine now that after the group enters the corridor, some of them, which have more "affinity" for the shops, stay longers looking the windows or buying stuff. Those who do not have any interest in this stuff, arrive faster in the restaurant.

Some people who don't have any interest at all, arrive without even  looking at the windows. They are the Dead Time Marker.

The group, starts to walk and some friends start to look and spent more time at certain shops, and they then divide into the clothes and book groups. The clothes group takes longer at the shops and is the last to reach the back. The books group arrives before them, but much later than the Dead Time Marker group.

This is the separation.

The solvophobic Theory

Although not accepted today, the solvophobic theory can also be explained in the “shopping model”.

It was created long ago by Csaba Horváth one of fathers of modern HPLC and explains the mechanisms of retention on reversed-phase liquid chromatography, where the mobile-phase is polar and the stationary phase is non-polar.

In the Solvophobic model, the Stationary Phase plays a less important role in separation. It was believed that analytes tend to adsorb in the stationary phase due to their incapacity to be solvated or form a cavity in the strong polar solvent

Now re-thinking this in our shopping mall: our group of friends just don't feel confortable in the crowd that try to push them forward. So they rest at the shop windows where they are less stressed, pushed or whatever.

 Peak Fronting

Just imagine the clothes group being attracted by a huge shop with special prices. Almost all the friends got in front of the shop but there is no space enough for all of them. Due to the traffic of people in corridors, the people that are in the back row can’t stand there too long, so the moving crowd going to the restaurants pushes the girls to the next shop with clothes. Basically there’s no enough space for all of them to express their attraction for the itens or check the prices.
I'm just talking about an overloaded situation, in which chromatography generates the famous Shark shaped peak.

Peak Tailing

Peak tailing is caused by a secondary interaction of analyte with something in the stationary phase, the most traditional situation is with an amine compound interaction with a free silanol in the Stationary Phase.
Imagine that our “model” group of  friends is interested in shopping for clothes, but  they also see some shoes shops on the way, so the group goes from one clothes store to another, but when they cross the shoes store some people are delayed and the "pack" of people on corridor start to be more spread out. 

Ion Pair Retention

There are two models for ion pair chromatography. First say that the analyte compound , in this case the people, combines by means of electrostatic forces to a counter ion and both are retained in the  hydrophobic stationary phase. Second model says that the counter ion is retained on the surface of hydrophobic stationary phase and then it retains the analytes, like in a dynamic ion-exchange chromatography.

Both theories can be described here. In the first, let's imagine the ion pair as a real couple that is formed when the group is in the crowd. The couple then moves to the shops looking for something they have in common, like sports. In the second situation, the group passes and they meet with another group standing in front one of the shops, after a fast chat, they start to walk again and meet with another group in front of another shop.

Scientifically speaking, it's not a perfect description. But at least, it's funny.